Photolithography
Photolithography – Pattern Transfer in Semiconductor Fabrication
Photolithography is a critical process in semiconductor manufacturing used to define micro- and nano-scale patterns on a wafer surface. It enables the transfer of complex circuit layouts from a mask (reticle) onto a wafer, forming the foundation for transistors, interconnects, and other integrated circuit (IC) features.
Photolithography is the heart of modern chip fabrication, enabling shrinking feature sizes, multi-layer stacking, and precise alignment, especially for sub-7nm and EUV (Extreme Ultraviolet) nodes.
Process Overview:
The photolithography process involves several precise steps:
Wafer Cleaning:
- Removes particles, organic contaminants, and moisture using wet or dry cleaning.
Photoresist Coating (Spin Coating):
- A thin, uniform layer of photoresist (light-sensitive polymer) is applied via spin coating.
- Thickness typically ranges from 100 nm to 2 µm, depending on the feature size.
Soft Bake (Pre-bake):
- Evaporates solvents from the resist layer to enhance adhesion and stability.
Mask Alignment & Exposure:
- A photomask containing the desired pattern is aligned over the wafer.
- Light (typically UV or EUV) is projected through the mask, exposing the photoresist.
Positive resist: Exposed regions become soluble.
Negative resist: Exposed regions become cross-linked and insoluble.